Stock GE7 to XTS Version?

[joelorigo]

If I understand some posts I saw earlier, the the new Efffects Layouts EQ (Boss GE7) could be modded to be the XTS modded GE7?

PRISMATIC EQ – Effects Layouts

XTS Midrange Graphic Modded GE-7

The XTS Midrange Graphic Mod was developed with Tom Bukovac. The session ace wanted an eq pedal centered entirely on the guitar's midrange frequencies. To that end, we take a full-range Boss GE-7 graphic eq and modify the frequency bands to focus on critical midrange frequencies. With the...

xacttone.com

 

[Guardians of the analog]

try using this. I haven't done it myself but it's not too difficult to figure out how to change each band

6 Band EQ formula?

Yes, i do have a 7 band eq, Danelectro Fish and chips. Using the calculator link, i came up with the cap values to get 160hz, and 600hz. I do not know much about the Q filter, but changing these same values from C1 to C2 really changes the Q. See attached:

forum.pedalpcb.com

 

[joelorigo]

Thanks. If I'm doing this right these are the corresponding parts in this small section of the Prismatic schematic, correct? If so, and I plug those numbers into the calculator, it comes up with 3304.71Hz, so 3.30471kHz. The frequency on that slider is labeled as 3.2 so that's pretty close.

 

[Guardians of the analog]

Looks like your doing it right, just gotta do them all now.

 

[joelorigo]

The real question is what to change to make the stock frequencies closer to the XTS modded one. Using that pot as an example, the corresponding on on the XTS is 2.5k vs 3.2k on the stock Boss. If I raise the value of R1 in the calculator, the frequency goes down. A 130k or 150k resistor there puts the frequency just below and above the 2.5k target. Is that all there is to it?

 

[Guardians of the analog]

I'm not sure if they changed the Q of the band. The only ones you need to figure out are 1.2k and 2.5 k. between the bass version and guitar version, all those values are in the build doc. How close is close enough too you? It depends on the tolerances of the parts. the calculator is using exact values and you would have to measure everything before using and I doubt they do that when they mod. If you can get really close to those values, say within 10-20% I would say you are good.

 

[joelorigo]

Yes I agree. 10-20% is definitely close enough for me. It's 1.2k, 2k, 2.5k and 4k which are the different frequencies on the XTS one so I see what you are saying that the others are already there in the schematic. I would just move their position.

The one thing is, in the schematic for the Prismatic, the first pot (6.4k), doesn't look exactly like the rest of the pots. Just to be clear, is R17 and C10 the R1 and C2 in the calculator? Where's the R2 and C1 in the schematic for that pot?

 

[joelorigo]

I have used the Bandpass EQ calculator to modify the frequencies of the pots of the Effects Layouts Prismatic EQ. Plugging the part values in to the calculator gives me frequency numbers (dark blue on my screenshot below) close to the target frequency (light blue) on the XTS version.
How do I use the calculator for the first pot, the highest frequency? There is only 1 capacitor and 1 resistor in front of that pot in the schematic.

 

[joelorigo]

Just bumping this.

 

[Guardians of the analog]

I have used the Bandpass EQ calculator to modify the frequencies of the pots of the Effects Layouts Prismatic EQ. Plugging the part values in to the calculator gives me frequency numbers (dark blue on my screenshot below) close to the target frequency (light blue) on the XTS version.
How do I use the calculator for the first pot, the highest frequency? There is only 1 capacitor and 1 resistor in front of that pot in the schematic.

@Chuck D. Bones can you help answer this? I'm not sure the best course of action with this one.

 

[DGWVI]

I have used the Bandpass EQ calculator to modify the frequencies of the pots of the Effects Layouts Prismatic EQ. Plugging the part values in to the calculator gives me frequency numbers (dark blue on my screenshot below) close to the target frequency (light blue) on the XTS version.
How do I use the calculator for the first pot, the highest frequency? There is only 1 capacitor and 1 resistor in front of that pot in the schematic.

68n and 560r are what are used in Boss's GE-7B for the 4k band

 

[joelorigo]

68n and 560r are what are used in Boss's GE-7B for the 4k band

Hmmm. I wonder if changing C10 and R17 in the above schematic to those values would give something close to 4k?

 

[DGWVI]

Hmmm. I wonder if changing C10 and R17 in the above schematic to those values would give something close to 4k?

Running the stock values through a calculator say that they don't actually provide 6.4k, but rather 4.1k.
Running the GE-7B values gives about the same frequency cutoff, but with slightly higher gain

That particular control is similar to a Tube Screamer tone control, so the low end of the pots sweep offers up a passive LPF, while the higher reaches are an active HPF.

Here's the calculator I used

 

[joelorigo]

Running the stock values through a calculator say that they don't actually provide 6.4k, but rather 4.1k.
Running the GE-7B values gives about the same frequency cutoff, but with slightly higher gain

That particular control is similar to a Tube Screamer tone control, so the low end of the pots sweep offers up a passive LPF, while the higher reaches are an active HPF.

Here's the calculator I used

Thanks, but I don't know what to do with that calculator! But if you say that that is going give you 4.1k instead of 6.4k I believe you. My question is then is there something before that in the signal flow making it 6.4k? In the upper row on the schematic? That all is before the lower row, right? Seems weird that Boss would say it was 6.4 if it wasn't.

 

[DGWVI]

Thanks, but I don't know what to do with that calculator! But if you say that that is going give you 4.1k instead of 6.4k I believe you. My question is then is there something before that in the signal flow making it 6.4k? In the upper row on the schematic? That all is before the lower row, right? Seems weird that Boss would say it was 6.4 if it wasn't.

Here's a prior thread also mentioning the cutoff frequency being closer to 4k than the labelled 6.4k. The two gain stages preceeding the EQ portion have fairly flat frequency responses

For the calculator, use the right hand side of this image as an example -

Select these options-

Which gives us -

 

[joelorigo]

Here's a prior thread also mentioning the cutoff frequency being closer to 4k than the labelled 6.4k. The two gain stages preceeding the EQ portion have fairly flat frequency responses

For the calculator, use the right hand side of this image as an example - View attachment 50965

Select these options- View attachment 50966View attachment 50967

Which gives us -
View attachment 50968

Oh wow that thread is interesting. I sure am not in a position to questing the above math, so I guess Boss is telling a little fib with that 6k slider.

I guess I will post this one more time for clarification. If I build the the Effects Layouts Prismatic EQ (based on the GE7), and change the values of the components I have in green, the results should be pretty darn close to the XTS GE7 version, yeah?

 

[bauerma4]

Wondering if you went through with the mod yet?

 

[joelorigo]

I have not. I have been building some other things that were in my stack of PCBs. Plus, I don't feel like I got a response in this thread that said definitely the modified schematic I shared was correct, and I don't know what I'm doing!!!

Still interested in it though. I have an Analogman modded GE7 so I'd like to try the more mid focused XTS version.

 

[bauerma4]

I’m interested in this mod as well, yet also don’t know how to do the calcs! It’s a great mod though, seeing as though you can buy a used GE-7 and complete this mod plus an upgrade to op-amps and have a great pedal under $100.

 

[joelorigo]

I've been focused on some pre-planned builds and life stuff to focus on this. I THINK I the mods I did are right using the calculator in the linked thread in post #2 of this thread. But it all seems too easy , there often is something a noob like me didn't know about or didn't know.
Plus there was an unresolved discussion about making the 6.4k pot into a 4k. It's possible it actually is already that, maybe...
I don't know, this above my level.